Electrical/pyrotechnic igniters in gas generators for impact protection systems (such as vehicle air bags and belt tensioning means) are generally known, as exemplified by DE-C1-41 02 275.
while the use of electronic igniting devices in vehicles has spread, so has the use of mobile radio equipment, resulting in the increased risk of momentary voltage surges in the vehicle electrical system which can activate an unprotected gas generator. For this reason, special measures are necessary so that any uncontrolled voltage peaks occurring in the vehicle electrical system does cause the triggering of the protection system.
DE-A1-34 15 625 discloses a high tension igniter with a predetermined spark gap. Circular and linear cutouts are provided in a metal layer and are connected to hollow pieces placed on planar manner, and are intended to serve on the one hand as voltage surge diverters and on the other hand as ignition bridges. The assembly is joined together by means of insulating rings and melt-type adhesives.
Such a construction requires the use of complicated photoetching processes or expensive laser cutting equipment to produce the required gap-shaped cutouts. Moreover, there is a risk of high electrostatic charges cutting through the insulating adhesive provided and inadvertently igniting an adjacent igniting composition which forms the highly explosive detonator.
Additionally, U.S. Pat. No. 5,109,772 discloses that a mixture of boron potassium nitrate, identified as BKNO.sub.3 is a rapid ignition means for pyrotechnic fuel and as such may be used for the propagation of the ignition of gas-generating materials, such as may be used for inflating air bags. In order to achieve the desired effect, BKNO.sub.3 is applied over a large surface distributed along the entire gas generator. Plates forming chambers are coated in the same manner. Coating is achieved by dipping the corresponding mechanical parts in an aqueous BKNO.sub.3 solution, with a subsequent drying procedure. This type of gas generator is ignited by a conventional thermo-electric igniter. Such a construction is relatively complicated and produces only an improved flaming distribution to a gas generator which has already been ignited.
In the course of further technical developments of air bags and pyrotechnically activated belt tensioning means, it has been found that known systems cause pressure pulses on ignition, can have a negative effect on gas propagation and an adverse influence on the desired gentle inflation of the air bag, or can cause mechanical overloads. Similar results can occur in the case of pyrotechnic belt tensioning means, where the pump plunger can be acted upon too quickly by the gas generation.
It is thus the object of the present invention to eliminate disadvantages of the known art and to provide a gas generator igniting capsule of a type which adequately increases the triggering and operational reliability of air bags and pyrotechnic belt tensioning means and the like and prevents the generation of compressed gas in a manner which would be dangerous, undesired and/or excessively harsh and thus also hazardous to the system in which the gas generator is employed.
The invention contemplates an igniting capsule having a resistive electrical igniter of defined resistance joined to at least one contact pin. A conductive ring encircles the contact pin and is spaced from the contact pin to produce a defined gap therebetween. The ring serves as a counter electrode to shunt voltage surges to earth. The igniter is in contact with a layer of a multilayer detonator charge. The contact pin defines a plug-like connection for interconnection with an electrical input line.
The subject of the present invention is capable of being integrated into known apparatus for increasing the safety of the occupants of a vehicle or aircraft in which the apparatus is employed.
The structural elements forming the apparatus are capable of being integrated into the igniter easily and without positioning aids. Sensitive insulating layers, insulating adhesives and the like which are also detrimental to mass production are eliminated.
The arrangement of the electrically conductive parts of the present invention insures that any voltage surge is diverted to ground and is thus made harmless. At the same time, the utilization of at least two different detonators enables the igniter chain to be matched to a proper detonation rate for the engineering of the system in the region of priming. In practice, the use of two detonators in the igniter primarily results in reliable ignition of a first detonator layer and then propagation of the ignition at a reduced ignition rate in a second, less highly explosive detonator layer. As a result of the two detonator layers being pressed together, the desired priming effect is also produced in the less highly explosive detonator.
In a preferred embodiment a galvanically conductive ring is constructed with sharp edges so that any sparkover takes place at a site defined by the partially increased field strength resulting from such a construction. The combination of the galvanically conductive ring with a seal is particularly convenient, since it reduces the structural height of the igniter. The bore of the ring may be frustoconical.
Mechanical integration of the contact pins into the plug socket reduces the necessary dimensions and at the same time provides for improved axial guidance of the pins.
Peripheral contact with the conductive ring can be employed to establish electrical connection therewith. Alternatively, the ring can be placed on a flange of the metal igniter housing so that the structural height of the igniter is additionally reduced. A ring structure which projects by means of contact faces out of a housing made of synthetic material and is contacted by a conductive gas generator housing is particularly preferred.
The use of lead styphnate as a first detonator provides the necessary reliability for ignition, even in combination with further detonators which are not highly explosive. BKNO.sub.3 in processed form has proved extremely favorable as the second detonator. The ratios of the two detonators may be varied in accordance with required pressure levels. In addition, the mixing ratio of BKNO.sub.3 can be adapted to a desired optimum pressure curve, while the particle size of the lead trizinate can be varied to obtain improved functional reliability. The controlled selection of the particle sizes or crystals of the BKNO.sub.3 mixture also serve to improve the quality of the ignition procedure.